fix: share compatible Collector materializations across query roots

[zzylol]

Migration slice A

Implements the first physical-sharing safety slice of #512.

• Emit one Collector materialization for compatible consumers of the same physical state, matching existing backend/precompute deduplication.
• Reject conflicting implementation, layout, lifecycle, or evidence contracts before publication; retain existing runtime-policy conflict checks.
• Normalize rate to its actual increase state algorithm while retaining separate query readouts.
• Preserve all consumers in plan identity despite producer deduplication.

Validation

Control-plane library tests pass, including shared quantile consumers in both profiles, conflicting implementations/layouts, separate sources, rate/increase state reuse, and consumer-sensitive plan identity.

Remaining scope

This is physical contract consistency, not workload-wide CSE/aggregate fusion or runtime update-count acceptance. Different evidence contracts conservatively fail closed rather than being silently merged.